It is known to propel a boat or other watercraft using a water jet apparatus mounted to the hull, with the powerhead placed inside (inboard) the hull and an axialflow water jet apparatus mounted outside the boat below the waterline. The drive shaft of the water jet apparatus is coupled to the crankshaft of the motor. The water jet apparatus comprises an impeller mounted on the drive shaft and a housing surrounding the impeller. The interior surface of the housing defines a water tunnel. The impeller is designed such that during motor operation, the rotating impeller impels water rearward through the water tunnel and out an exit nozzle. The reaction force of the rearward water flow exiting the jet propulsion device propels the watercraft forward.
To facilitate use of jet-propelled boats in shallow water, it is known to mount the water jet propulsion unit at an elevation such that the propulsion unit does not project below the bottom of the boat hull. This can be accomplished, for example, by installing a duct in the stern of the boat, the duct being arranged to connect one or more inlet holes formed in the bottom of the hull with an outlet hole formed in the transom. The pump jet is then installed outside the hull in a position such that the pump jet inlet is in flow communication with the duct outlet at the transom.
Typically the jet drive power plant is mounted on stringers built into the hull of a boat for in-line drive applications or on an adapter plate mounted to stringers for 90.degree. drive applications. It is also known to mount a marine engine to the inboard or forward face of a transom in a cantilever arrangement. In such a cantilevered arrangement, it is conventional practice to provide a hole in the transom through which the engine drive shaft passes.
There is a need for a design whereby a water jet propulsion unit is powered by an engine cantilevered from the transom. The mounting arrangement should also incorporate means for venting exhaust gases from the engine to a locus below the waterline and behind the transom.